DESIGN OF A GAS-FIRED CARBON-AMMONIA ADSORPTION HEAT

PUMPSteven Metcalf, Ángeles Rivero Pacho, Bob Critoph

University of Warwick

i-STUTE, 9 March 2018

• Box-for-box exchange for conventional gas boiler Retrofit market (> 90% of annual sales)

• Air source• 30% reduction in gas consumption• 7-10 kW (UK, 3 bedroom semi-detached house)

Heat pump concept

Schematic drawing

Gas Burner

Hot Gases

Air-to-Pressurised Water Heat Exchanger

Warm Exhaust Gases

Inlet Air

Final Exhaust Heat Exchanger

AdsorbentBed 1Heated

AdsorbentBed 2Cooled

Condenser

Evaporator

Cooled Air from Evaporator

Return water from house

Ammonia

Cool Exhaust Gases

Ambient Air to Evaporator

Heated water to house

Focussing only on adsorption heat pump development

Previous Generator Design

Shell and tube heat exchanger

150 mm

40

0 m

m

0.8 mm

3 mm1.2 mm

Experimental Results (June 2016)

Experiment Model

Cycle Time

[s]

Load Inlet [°C]

Load Outlet

[°C]

Evaporating Temperature

[°C]COP COP

480 26.2 31.7 3.2 1.34 1.33

420 27.1 33.1 0.1 1.32 1.31

420 28.2 34 3.7 1.33 1.3

480 28.8 35.1 -1.6 1.3 1.3

420 32.9 37.9 3.9 1.255 1.29

360 33.4 38.8 4 1.23 1.27

540 37.6 42.7 1.9 1.244 1.25

480 38 43.4 1.8 1.233 1.25

300 40.5 46.7 3.5 1.19 1.21

Heating Power: 7.5 – 9 kWCOP: 1.19 – 1.34

Conclusion:

Machine performed as predicted,however, high manufacturing cost of the generators prohibited further development.

New Generator Design

Shell and Finned Tube

Design Parameters:

• Tube diameter

• Tube pitch

• Carbon thickness

• Fin thickness

• Turbulator tube insert

Detailed simulations in Matlab

New Generator Design

Target Performance:

• Heating Power 10 kW

• Total Generator Volume ≤10 litres

• Internal COP≥1.4

Performance Predictions

Large Temperature Jump Test100 mm Long Test Sample

Large Temperature Jump Test

Vessel (Ammonia

Gas)

TP

T T

Water Flow

Large Temperature Jump Test

Match obtained between experiment and model predicted pressure rise

Time constant ~50 seconds

Machine Construction

Hot off the press…

Machine Construction

GeneratorsEvaporator

Condenser

Water valves

Water pumps

Ammonia Check Valves

Machine Testing

System of Heating and Cooling Baths to provide:

- Up to 170°C Pressurised Water for High Temperature Heat Input

- 10 kW of heat rejection for the condenser and cooler

- Glycol flow down to -10°C for evaporator

Conclusions

• Finned tube generator designs investigated with MATLAB model

• Performance verified with a sample section tested with the large temperature jump method

• Complete machine under construction as a test bed for generator and diverting valve designs

Further Work• If the generator design gives promising results, the unit will

be packaged more compactly.

• A gas burner and air-source evaporator would be added and testing carried out in an environmental chamber.

Thanks for your attention!